hv_netvsc: drop common code until callback model fixed

The callback model of handling network failover is not suitable
in the current form.
  1. It was merged without addressing all the review feedback.
  2. It was merged without approval of any of the netvsc maintainers.
  3. Design discussion on how to handle PV/VF fallback is still
     not complete.
  4. IMHO the code model using callbacks is trying to make
     something common which isn't.

Revert the netvsc specific changes for now. Does not impact ongoing
development of failover model for virtio.
Revisit this after a simpler library based failover kernel
routines are extracted.

This reverts
commit 9c6ffbac ("hv_netvsc: fix error return code in netvsc_probe()")
and
commit 1ff78076

 ("netvsc: refactor notifier/event handling code to use the failover framework")

Signed-off-by: Stephen Hemminger <sthemmin@microsoft.com>
Signed-off-by: David S. Miller <davem@davemloft.net>